Conventional equipment for measuring quantities associated with the operation of a high-voltage overhead line usually utilizes, for variables to be measured, separate means for transforming the measured quantity, as for instance current or voltage, into corresponding analog quantity at the ground potential indicating the measured quantity. Voltage measurements are usually accomplished by the use of high-voltage dividers, and current measurements usually by step-down transformers. The measurement of current flow in a high-voltage conductor, as known from the U.S. Pat. No. 2,724,821, can also be accomplished by high-frequency transmitter, modulated by current in that conductor. This kind of current measurement employs less bulky and expensive equipment than are step-down current transformers, but still preserves their functional characteristics with respect to signal form at the ground potential.
As known from the U.S. Pat. No. 3,488,591, there also exists means for obtaining analog signals at the ground potential corresponding to current and voltage but only in connection with a bushing supporting a high-voltage line as such measuring means requires to measure quantity proportional to field. Such means cannot be used for measuring voltages and currents in an arbitrary point on the high-voltage overhead line.
The use of keying in discrete aural pulses, where the keying frequency is in discrete relationship with the measured values, is described in the U.S. Pat. No. 2,287,786. This kind of solution of the problem does not represent measured quantities as digital data neither are the measured quantities transferred as digital data.
The number of variables in conventional measuring equipment is usually limited to current and voltage and it usually relates to their RMS values regardless of the fact that it is highly desirable to obtain also some other values related with a variable.
As an example for the current flow in an AC high-voltage overhead line, it is desirable to obtain accurate data not only about its RMS value or its peak value, but also the indication of time the current crosses the zero point, the data about composition of the higher harmonics, data related to transients, and other data, if needed.
In summary, the conventional equipment does not allow the complex measurement of quantities associated with the operation of a high-voltage overhead line on that same line and on its potential, it neither allows a real time acquisition of data with the aim to present the operational status of the high-voltage overhead line like a data telegram transmissible wirelessly to a remote point.